Method for hand-over of terminal, network element, base station, and communication system

ABSTRACT

The invention provides a method for hand-over of a terminal from a first base station to a second base station, radio network element, terminal, base station and a communication system. The method for hand-over of a terminal from a first base station to a second base station, wherein said first base station is EV-DO enabled in an access network and said second base station is not EV-DO enabled, said method comprising: transmitting an EV-DO pilot signal from said second base station to said terminal; sending a route update message including an EV-DO pilot strength from said terminal if said EV-DO pilot strength is above a predetermined threshold; calculating a CDMA pilot strength based on said EV-DO pilot strength; and performing the hand-over of said terminal to said second base station when CDMA pilot strength is above the hand-over threshold.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to radio communication, in particular, tomethod for hand-over of a terminal, network controller element,terminal, base station, and communication system.

BACKGROUND OF THE INVENTION

CDMA 20001x is a version of CDMA 2000, which utilizes both circuitnetworks and packet networks and provides voice service and low-ratedata services with a maximum transmission data rate of 307.2 Kbps. CDMA2000 1xEV-DO is a data-optimized evolution of the CDMA2000 1x standardwith High Rate Packet Data (HRPD) technology, which is dedicated for apacket network to transmit only data and provides bi-directionalhigh-rate data services with a maximum transmission rate of 2.4 Mbps.Its evolution of EV-DO RevA has the maximum forward link data rate of3.07 Mbps and maximum reverse link data rate of 1.8 Mbps. Moreover,EV-DO RevA has the capability to support VoIP service. By time-dividingradio channel into separate pilot, MAC and data channels, EV-DO, whichuses a 1.25 MHz data channel, improves spectrum efficiency andeliminates the interference increase that voice traffic would cause dataspeed to drop.

Hereinafter, the CDMA 2000 1x system is simply referred to as “1xsystem” or “CDMA system” and the CDMA 2000 1xEV-DO RevA system is simplyreferred to as “EV-DO system” for the convenience of explanation.

Currently, the EV-DO network has generally been used together with theconventional 1x network. More specifically, the EV-DO network may onlycover some cities, or hot spots, whereas the conventional 1x networkcovers almost everywhere to form a seamless radio data network. Thus,the handoff from VoIP in EV-DO system to 1x circuit voice becomes veryimportant for keeping the voice call continuity.

The existing hand-over from 1xEV-DO to 1x system is related to CircuitServices Notification Application (CSNA). CSNA has been introduced inthe EV-DO system to address operation of an Access Terminal/MobileStation (AT/MS) that otherwise would have to periodically retune to the1x system to check for pages while it is monitoring the EV-DO system.For CSNA, the AT (a device providing data connectivity to a user, whichis equivalent to a mobile station in 1x systems.) and the AN (AccessNetwork, a logical entity in the Radio Access Network (RAN) used forradio communications with AT.) implement a filtering mechanism to allownotifications associated with certain services to be tunneled between 1xand EV-DO systems.

The handoff procedure from 1xEV-DO to 1x system defined in 3GPP2A.S0008-B as follows:

-   -   (1) AN receives a Route Update Message (RUM) for reporting the        current link status including the pilot strength, pilot phase of        each pilot in active set and neighbor set from an AT/MS, and        finds the current pilot strength (Ec/Io) for the EV-DO cell is        lower than a predetermined threshold and cannot maintain the        VoIP service quality.    -   (2) AN sends the 1X overhead messages to AT/MS through CSNA        protocol.    -   (3) AN sends the 1X service redirection message to AT/MS through        CSNA protocol. This will indicate the AT/MS to begin the        procedure to move the call from VoIP of 1xEV-DO to circuit voice        of 1X.    -   (4) AT/MS send the 1X origination to AN through CSNA.    -   (5) AN sends the handoff direction message to MS/AT.    -   (6) MS/AT tunes to 1X channel to continue the call.

Whereas 1x pilot is transmitted continuously, the EV-DO pilot burst has96 chips duration with only one pilot burst for each half slot.Consequently, the RUM sent by the AT in EV-DO system only includes EV-DOpilots in current system. Thus, the pilot measurement for the 1X systemis not performed and the AN cannot know clearly what is the CDMAcandidate in fact.

Compared to a current handoff procedure, the VoIP to 1X circuit voicehandoff has no pre-provisioning candidates to perform its blind handoff.Therefore, the AN has to determine the active set of 1X system based onthe 1X sector information provided by the CSNA protocol during thehandoff procedure. The AN will get the 1X neighbor list and sort thelist based on the number of occurrence in the overhead messages. Thenthe 6 pilots of the font candidates of the list becomes the active setof the 1X system.

Since the generated handoff candidates are based on the possibilities ofoccurrence in the overhead message, and not on the real measurement, thesuccessful handoff cannot be assured. Actually this process cannot tellwhich CDMA cells have the best coverage for the AT, and it is possiblethat a CDMA cell has the good coverage but is missed because only 6pilots are allowed in the active set. Thus the call drop may happenduring the handoff.

In addition, another issue for the current system is the “Near-FarInterference” between the border of EV-DO system and 1x system. TheEV-DO system is time divided system in the forward link. And the pilotchannel transmission is synchronized for the whole system, thus a pilotsignal from the neighbor EV-DO cell is the main interference for theEV-DO system. When a cell is a border cell of the EV-DO system, thepilot strength thereof may be near 0 dB since there is no interferenceof neighbor cell. Therefore the AT in the border EV-DO cell can maintainthe link further than in the normal EV-DO cell. Thus there is thepossibility that the AT eventually is very near to the CDMA cell when ittries to maintain the long EV-DO traffic link. Then the transmitter ofthe AT may cause an interference with the reverse link of the CDMA cell,which is called the “Near-Far Interference between EV-DO and CDMA”. Itpotentially may decrease the CDMA cell's capacity. Of cause, theinterference effects are a function of the spectral location of CDMA andEV-DO carriers, for example, the worst interference impact comes fromthe EV-DO channel spectrally adjacent to a CDMA channel.

SUMMARY OF THE INVENTION

To solve the above problem in the prior art, the invention provides amethod for hand-over of a terminal from a first base station to a secondbase station, a network element, a hybrid terminal, a device, basestation and a communication system.

According to one aspect of the invention, there is provided a method forhand-over of a terminal from a first base station to a second basestation, wherein said first base station is EV-DO enabled in an accessnetwork and said second base station is not EV-DO enabled, said methodcomprising: transmitting an EV-DO pilot signal from said second basestation to said terminal; sending a route update message including anEV-DO pilot strength from said terminal if said EV-DO pilot strength isabove a predetermined threshold; calculating a CDMA pilot strength basedon said EV-DO pilot strength; and performing the hand-over of saidterminal to said second base station when said CDMA pilot strength isabove the hand-over threshold.

According to another aspect of the invention, there is provided anetwork element for controlling hand-over from a first base station to asecond base station, wherein said first base station is EV-DO enabled inan access network and said second base station is not EV-DO enabled,comprising: calculating unit configured to calculate a CDMA pilotstrength based on an EV-DO pilot strength of said second base station;determining unit configured to determine whether said CDMA pilotstrength is above a hand-over threshold; and performing unit configuredto perform the hand-over of a terminal from said first base station tosaid second base station when said CDMA pilot strength is above thehand-over threshold.

According to still another aspect of the invention, there is provided ahybrid terminal for use in a CDMA system and an EV-DO system, whereinsaid hybrid terminal is configured to receive an EV-DO pilot signal fromsaid CDMA system.

According to still another aspect of the invention, there is provided adevice for generating a pilot signal, which is to be equipped with anon-EV-DO enabled base station in a CDMA system, wherein said device isconfigured to generating a EV-DO pilot signal.

According to still another aspect of the invention, there is provided abase station in a CDMA system, which is not EV-DO enabled, comprisingthe above-described device for generating a pilot signal.

According to still another aspect of the invention, there is provided acommunication system, comprising: the above-described hybrid terminal,the above-described base station in CDMA system, and the above-describednetwork element for controlling hand-over.

BRIEF DESCRIPTION OF THE DRAWINGS

It is believed that the purposes, features and advantages of the presentinvention will be better understood from the following description ofthe detailed implementation of the present invention taken inconjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of the communication systemaccording to an embodiment of the present invention;

FIG. 2 shows a schematic block diagram of the network element accordingto another embodiment of the present invention;

FIG. 3 shows a flow chart of the method for hand-over from EV-DO systemto 1x system according to another embodiment of the present invention;

FIG. 4 shows a structure of EV-DO pilot channel in EV-DO system;

FIG. 5 shows a structure of EV-DO time slot;

FIG. 6 shows a schematic block diagram of a device for generating EV-DOpilot in 1x system according to another embodiment of the presentinvention; and

FIG. 7 shows a schematic block diagram of a device for generating EV-DOpilot in 1x system according to still another embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Next, various embodiments of the present invention will be described indetail in conjunction with accompany drawings.

FIG. 1 shows a schematic block diagram of the communication systemaccording to an embodiment of the present invention.

As shown in FIG. 1, the communication system 10 comprises CDMA system20, EV-DO system 30 and an AT/MS 40. For the convenience of description,1x system 20 includes only one base station (BS) 202 with B cell 202A 1xonly enabled, and the EV-DO system 30 includes Access Network (AN) 302with A cell 302A of combined 1x and EV-DO RevA, and AN 304 with C cell304A of combined 1x and EV-DO Rev0. VoIP call is supported in cell 302A,while is not in cell 304A. And those skilled in the art may appreciatethat these systems may include more than one base station and AN infact.

AN 302 comprises a network controller element 306 which may controlhand-over from an EV-DO system to a 1x system.

FIG. 2 shows a schematic block diagram of the network controller elementaccording to an embodiment of the present invention.

Referring to FIG. 2, the network controller element 306 comprisescalculating unit 3002, for calculating a CDMA pilot strength of a CDMAcell based on its EV-DO pilot strength; determining unit 3004, fordetermining whether the CDMA pilot strength is above a hand-overthreshold or not; and performing unit 3006, for performing the hand-overof a terminal from the EV-DO system to the 1x system when the CDMA pilotstrength is above the hand-over threshold. In addition, the networkcontroller element 306 further comprises maintaining unit 3008, formaintaining a pilot PN mapping table for the 1x and EV-DO system for thesame CDMA cell site.

FIG. 3 shows a flow chart of the method for hand-over from EV-DO systemto 1x system according to an embodiment of the present invention.

As shown in FIG. 3, in the step S110, the CDMA base station 202 at theborder of CDMA and EV-DO coverage can generate an EV-DO pilot signal,and transmit the EV-DO pilot signal to an AT/MS 40 in the step S120. Andthe power of the pilot is the same as the other normal EV-DO cell'spower. It is the basis on which reliable handoff can be performed. Thatis, AN 302 may know that there exists a CDMA cell through EV-DO pilottransmitted from 1x cell 202A.

In a subsequent step S130, when the EV-DO pilot strength is above apredetermined threshold, the AT/MS 40 sends Route Update Message (RUM)to the AN 302. RUM contains an EV-DO pilot strength concerning 1x cell202A, thus AT/MS 40 can trigger a reliable handoff by means of measuringEV-DO pilot and comparing its strength with a predetermined threshold.

Next, in the step S140, maintaining unit 3008 of network controllerelement 306 in EV-DO network may maintain a pilot mapping table for allthe border cells of the CDMA and DO systems, such as cell 202A. Thepilot mapping table includes at least, e.g. pseudo noise (PN) code, apilot code of CDMA and of EV-DO for each border cell.

For the CDMA only cell 202A, it may transmit an EV-DO pilot. As shown inTable 1, individual cell in the border of EV-DO system and 1x system hasboth the CDMA pilot PN and EV-DO pilot PN.

TABLE 1 Pilot Mapping table for CDMA and EV-DO Cell Number CDMA Pilot PNEV-DO Pilot PN 1 PN_(1X,1) PN_(DO,1) 2 PN_(1X,2) PN_(DO,2) . . . . . . .. . n PN_(1X,n) PN_(DO,n)

In step S150, calculating unit 3002 of network controller element 306may use the new algorithm to determine the pilot strength of the CDMAcell 202A based on the EV-DO pilot strength thereof. Therefore, the AN302 may determine whether a handoff from EV-DO to CDMA will happen ornot. The proposed algorithm is described in more detail in below.

Referring to FIG. 1, there are 3 cells in the system 10: cell A302A,cell B202A and cell C304A. The system capability can be described in thetable below:

TABLE 2 Border cells' Configuration Table Cell 1X Capability EV-DOCapability VoIP Capability Cell 302A Yes DO RevA Yes Cell 202A Yes DOpilot only No Cell 304A Yes DO Rev0 No

It is assumed that the path loss from each cell to AT/MS 40 is PL1, PL2,and PL3 (PLi<1) respectively, and that the CDMA carrier and EV-DOcarrier are the same band.

If the transmit power for EV-DO is P Watts, then the pilot strength forcell A302A can be expressed mathematically:

$\begin{matrix}{( {{Ec}/{Io}} )_{A,{DO}} = \frac{P*{PL}\; 1}{{P*{PL}\; 1} + {P*{PL}\; 2} + {P*{PL}\; 3} + {F*N_{th}*{BW}}}} & (1)\end{matrix}$

Here, F is the noise factor of the EV-DO cell,

-   -   N_(th) is thermal noise spectrum density,    -   BW is a bandwidth (1.23 or 1.25 mHz),    -   Ec/Io is the ratio of the combined pilot energy per chip Ec, to        the total received power spectrum density (noise and signals)        Io.

Since the thermal noise is relatively small compare to the signal andinterference, the EV-DO pilot strength can also be:

$\begin{matrix}{{( {{Ec}/{Io}} )_{A,{DO}} = \frac{P*{PL}\; 1}{{P*{PL}\; 1} + {P*{PL}\; 2} + {P*{PL}\; 3}}};} & (2)\end{matrix}$

The EV-DO and CDMA are assumed to use the same band, thus thepropagation modes are the same. For example, in 3GPP2 “CDMA2000Evaluation Methodology”, there is a propagation mode defined for 1.9 GHzas follows:The PathLoss=28.6+35 log 10(d) dB, d in meters.

(Bts Ant Ht=32M, Ms=1.5M)

Accordingly, the path loss for EV-DO and CDMA may be considered thesame, since the distance and RF environment for CDMA and EV-DO are thesame.

Firstly considering the EV-DO coverage for the system 10 as shown inFIG. 1, and the pilot in EV-DO being transmitted in full power P Watts,assume the AT carries the VoIP call in cell A 302A coverage movingtowards cell B 202A. The pilot strength for cell B 202A seen by AT is:

$\begin{matrix}{( {{Ec}/{Io}} )_{B,{DO}} = {\frac{P*{PL}\; 2}{{P*{PL}\; 1} + {P*{PL}\; 2} + {P*{PL}\; 3}} = \frac{{PL}\; 2}{{{PL}\; 1} + {{PL}\; 2} + {{PL}\; 3}}}} & (3)\end{matrix}$

And the pilot strength for cell C 304A is:

$\begin{matrix}{( {{Ec}/{Io}} )_{C,{DO}} = \frac{{PL}\; 2}{{{PL}\; 1} + {{PL}\; 2} + {{PL}\; 3}}} & (4)\end{matrix}$

Secondly considering for the CDMA coverage, assume:

(1) Call loads factor for cell A, B and C are β1, β2 and β3 (0βi<1)respectively;

(2) “f” is the fraction for the pilot power to the CDMA cell's maximumtransmitter power, and generally within the scope from 15% to 20%;

(3) P_(OH) is the power of the overhead channel of the CDMA cell 202A;

(4) P_(T) is the total traffic power available for the CDMA cell 202A;and

(5) Thermal noise for CDMA (−108 dBm) is neglected compared to thesignal and interference.

Referring to FIG. 1, the CDMA pilot strength for cell B 202A is:

$\begin{matrix}\begin{matrix}{( {{{Ec}/I}\; 0} )_{B,{1X}} = \frac{PilotPower}{{SignalPower} + {Interference}}} \\{{= \frac{f*( {P_{OH} + P_{T}} )*{PL}\; 2}{\sum\limits_{i}{( {P_{OH} + {\beta\; i*P_{T}}} )*{PLi}}}};}\end{matrix} & (5)\end{matrix}$

And also the pilot strength for cell C is:

$\begin{matrix}{( {{Ec}/{Io}} )_{C,{1X}} = \frac{f*( {P_{OH} + P_{T}} )*{PL}\; 3}{\sum\limits_{i}{( {P_{OH} + {\beta\; i*P_{T}}} )*{PLi}}}} & (6)\end{matrix}$

If the pilot strength in EV-DO system has the relationship blow:(Ec/Io)_(B,DO)>(Ec/Io)_(C,DO),

then the result PL2>PL3 can be obtained according to equation (3) and(4).

Therefore we can obtain as follows according to equation (5) and (6):(Ec/I0)_(B,1X)>(Ec/Io)_(C,1X)

That is to say, if the neighbor lists for both CDMA and EV-DO is sortedaccording to the pilot strength, the sequences are the same for CDMA andEV-DO. More specifically, the strong pilot in EV-DO system also means astrong pilot in CDMA system, and vice versa.

And also it is found that there is the further relationship betweenpilot strength for CDMA and EV-DO for the same sector.

The recommended handoff thresholds for CDMA and EV-DO are as follows:

TABLE 3 Recommended Handoff Threshold System type T_ADD (PilotAdd forDO) T_Drop (PilotDrop for DO) CDMA −13 dB −15 dB EV-DO  −7 dB  −9 dB

Taking the cell B 202A as the example:

$( {{{Ec}/I}\; 0} )_{B,{1X}} = {{\frac{f*( {P_{OH} + P_{T}} )*{PL}\; 2}{\sum\limits_{i}{( {P_{OH} + {\beta\; i*P_{T}}} )*{PLi}}} > \frac{f*( {P_{OH} + P_{T}} )*{PL}\; 2}{\sum\limits_{i}{\begin{pmatrix}{P_{OH} +} \\{{\beta max}*P_{T}}\end{pmatrix}*{PLi}}}} = \frac{f*( {P_{OH} + P_{T}} )*{PL}\; 2}{( {P_{OH} + {{\beta max}*P_{T}}} )*( {{{PL}\; 1} + {{PL}\; 2} + {{PL}\; 3}} )}}$

Here βmax is the maximum call load factor for cell A 302A, B 202A and C304A. From the equation (3), we can get:

$\begin{matrix}{( {{{Ec}/I}\; 0} )_{B,{1X}} > {\frac{f*( {P_{OH} + P_{T}} )}{P_{OH} + {{\beta max}*P_{T}}}*( {{Ec}/{Io}} )_{B,{DO}}}} & (7)\end{matrix}$

Here,

$\frac{f*( {P_{OH} + P_{T}} )}{P_{OH} + {{\beta max}*P_{T}}}$actually represents the minimum ratio of a pilot power to overall powerat antenna port in CDMA cell 202A. Thus, the CDMA pilot strength(Ec/I0)_(B,1X) can be estimated based on the EV-DO pilot measurement.

For example, if:

(1) βmax=0.5 with all the cells being half loaded;

(2) P_(OH) is 22% of the total power; and f=15%,

then

$( ( {{{Ec}/I}\; 0} )_{B,{1X}} )_{dB} > {{10*\log\; 10( \frac{0.15}{0.22 + {0.5*( {1 - 0.22} )}} )} + {( ( {{Ec}/{Io}} )_{B,{DO}} )_{dB}.}}$

So, ((Ec/I0)_(B,1X))_(dB)>((Ec/Io)_(B,DO))_(dB)−6 dB.

Consequently, if the Route Update Message sent from AT/MS 40 includes aEV-DO pilot with the pilot strength −9 dB, it also indicates that theCDMA pilot strength is −15 dB for the same sector. It means that theCDMA signal for the AT is also very strong and can be used for voiceservice.

Finally, in the step S160, when CDMA pilot strength is above a hand-overthreshold T_ADD, performing unit 3006 of network controller element 306in EV-DO network switches AT/MS 40 into the base station 202. Morespecifically, if the pilot of CDMA is strong enough, AN 302 sends the 1Xoverhead messages to AT/MS 40 through CSNA protocol; and AN 302 sendsthe 1X service redirection message to AT/MS 40 through CSNA protocol.This will indicate the AT/MS 40 to begin the procedure to move the callfrom VoIP to 1X circuit voice. Then the MS/AT 40 sends the 1Xorigination to AN 302 through CSNA. And AN 302 sends the handoffdirection message to MS/AT 40. Finally MS/AT 40 tunes to 1X channel tocontinue the call.

In the embodiments of the present invention, the EV-DO pilot transmittedby the CDMA base station 202 is included into the neighbor set of theborder EV-DO AN 302, thus the reliable hand-over can be achieved byimplementing EV-DO pilot measurement.

In another embodiment of the present invention, the base station 202 inthe border of EV-DO may comprise a device 204 for generating EV-DO pilotsignal.

As shown in FIG. 4, the pilot channel of EV-DO system consists ofall-‘0’ symbols transmitted on the I-channel with 16-chip Walsh cover 0at a fixed chip rate of 1.2288 Mcps. And groups of 16 slots align tosystem time on even-second ticks.

Following orthogonal spreading, the pilot channel sequence is combinedwith other channel sequences such as Ack and data channel, to formresultant I-Channel and Q-Channel sequences, and these sequences arequadrature spread, which is equivalent to a complex multiply operationof the resultant I-Channel and resultant Q-Channel sequences by the Ichannel PN sequence PNi and Q channel PN sequence PNq with also a fixedchip rate of 1.2288 Mcps. And the characteristic polynomials of PNsequences PNi and PNq are also defined as follows:P ₁(x)=x ¹⁵ +x ¹⁰ +x ⁸ +x ⁷ +x ⁶ +x ²+1

(for the in-phase (I) sequence)

andP _(Q)(x)=x ¹⁵ +x ¹² +x ¹¹ +x ¹⁰ +x ⁹ +x ⁵ +x ⁴ +x ³+1

(for the quadrature-phase (Q) sequence).

In order to obtain the I and Q PN sequences (of period 2¹⁵), a ‘0’ needbe inserted after 14 consecutive ‘0’ outputs (this occurs only once ineach period). Therefore, the PN sequences PNi and PNq have one run of 15consecutive ‘0’ outputs instead of 14.

Referring to FIG. 4, following the quadrature spreading operation, theimpulses of I and Q channels are applied to the inputs of the I and Qbaseband filters respectively. Then it will form a forward pilotbaseband signal by performing carrier modulation followed by beingconverted into analog signal, which can be combined to the transmit pathof base station in CDMA system.

The EV-DO pilot signal is defined in C.S0024-A as follows:the EV-DO pilot signal=(I−j*Q)*Walsh0*(PNi−j*PNq).

-   -   It can be known from FIG. 4 that the Walsh cover 0 is all 1, and        I data is all 1, Q data is all 0, so        EV-DO pilot signal=(PNi−j*PNq).

Furthermore, within each slot, the pilot of EV-DO system is timedivision multiplexed with all the other forward link channels, such asMAC channel and data channel. As shown in FIG. 5, each pilot slot isdivided into two half slots of 1024 chips, each of which contains apilot burst. And each pilot burst has a duration of 96 chips and becentered at the midpoint of the half slot.

Referring to FIG. 6, the device 204 to implement above-described conceptmay include: EV-DO PN generating module 206 to generate PN sequences PNiand PNq for both I and Q channels respectively, in connection withTiming Module 212 of said second base station which provides Even SecondTick System clock to the generating module 206 and channel gating module224, and with Controller 214 of said second base station whichconfigures for Pilot PN Offset and time advance Tx; base band filter 216and 218 which are individually configured to base band filter for I andQ PN sequences provided by generating module 206; carrier modulatingmodule 220 configured to carrier modulate the I and Q channel PNsequences for obtaining real pilot signal S(t); and channel gatingmodule 224 for generating 96 chips per 1024 chips within half slot,while the other chips being gated off.

The EV-DO PN generating module 206 comprises two phase-shift registersfor PNi and PNq respectively.

Furthermore, the device 204 may further include multiplier 222, whichmultiplies the real signal S(t) with pilot gain for power control, andis connected to the input of the gating module 224.

Finally, the EV-DO pilot baseband signal can be available from theoutput of the gating module 224.

The EV-DO pilot channel can alignment with the system even second tick,and the CDMA base station has the same timing source. So the EV-DO pilotcan be generated in the CDMA base station.

Alternatively, as shown in FIG. 7, the device 204 may include EV-DO PNgenerating module 206 which comprises the output judging module 226 and228 respectively for I and Q channel. The judging module 226 and 228 mayjudge the output for I and Q according to the system clock provided bytiming module 212, thus the chip is outputted transparently in the pilotburst time frame while the remainder is outputted as “0”. That is, only96 chips of every 1024 chips (half slot) may be outputted.

Also, the output of generating module 206 for I and Q channel areconnected to baseband filter 216 and 218 respectively, and by carriermodulating the real pilot signal can then be obtained.

Further, the device 204 may include the multiplier 222, which multipliesthe real signal S(t) with pilot gain for power control.

Using the timing source in CDMA base station, the EV-DO pilot signal canbe generated using the FPGA. It can be appreciated that the device forgenerating EV-DO pilot signal at CDMA base station can be implemented byhardware circuit such as Very Large Scale Integrated Circuit or gatearray, semiconductor such as logic chips and transistors, orprogrammable hardware device such as field programmable gate array,programmable logic device, and by software executing on various types ofprocessors, and by the combination of above hardware circuit andsoftware.

As described above, the proposed method in the present invention canminimize the interference to the CDMA network.

Similar to concept of calculating in the communication system 10, assumethe path loss of the EV-DO and CDMA combined cell is PL1, and the pathloss of the CDMA only cell is PL2 with the CDMA carrier and EV-DOcarrier having the same band.

If the transmit power for EV-DO is P Watts, then

$\begin{matrix}{( {{Ec}/{Io}} )_{DO} = \frac{P*{PL}\; 1}{{P*{PL}\; 1} + {F*N_{th}*{BW}}}} & (8)\end{matrix}$

Here, the define of F, N_(th), BW and Ec/Io is same as above.

F*N_(th)*BW is about −108.1 dBm if the noise figure of the cell is 5 dB,so it is relatively small. If the AT/MS is at the border of EV-DO cell,Ec/Io is about 0 dB from equation (8). Then the AT/MS can move away fromthe EV-DO cell. When the P*PL1 is near −108.1 dBm, the Ec/Io willdecrease. Assume P is 42 dBm(16 W), then the PL1 is 155 dB when theEc/Io is −6 dB. This path loss is at least 3 dB higher than the normallink budget. That is the reason why the AT/MS can maintain the EV-DOlink far away from the normal coverage.

If the CDMA cell also transmits the EV-DO pilot signal, then the AT/MSwill see a normal EV-DO coverage case. The pilot strength can beexpressed mathematically as follows:

${( {{Ec}/{Io}} )_{DO} = \frac{P*{PL}\; 1}{{P*{PL}\; 1} + {P*{PL}\; 2} + {F*N_{th}*{BW}}}};$

Since the thermal noise is relatively small, so the EV-DO pilot strengthcan also be:

$\begin{matrix}{{( {{Ec}/{Io}} )_{DO} = \frac{P*{PL}\; 1}{{P*{PL}\; 1} + {P*{PL}\; 2}}};} & (9)\end{matrix}$

It is the normal EV-DO coverage scenario and the “Near-Far Interference”issue can be resolved.

While the method for hand-over of a terminal from a first base stationto a second base station, network element, hybrid terminal, basestation, the device for generating a pilot signal, and the communicationsystem of the present invention have been described in detail with someexemplary embodiments, these embodiments are not exhaustive, and thoseskilled in the art may make various variations and modifications withinthe spirit and scope of the present invention. Therefore, the presentinvention is not limited to these embodiments; rather, the scope of thepresent invention is solely defined by the appended claims.

1. A method for hand-over of a terminal from a first base station to asecond base station, wherein said first base station is EV-DO enabled inan access network and said second base station is not EV-DO enabled,said method comprising: transmitting an EV-DO pilot signal from saidsecond base station which is not EV-DO enabled to said terminal; sendinga route update message including an EV-DO pilot strength from saidterminal if said EV-DO pilot strength is above a predeterminedthreshold; calculating a CDMA pilot strength based on said EV-DO pilotstrength; and performing the hand-over of said terminal to said secondbase station when said CDMA pilot strength is above the hand-overthreshold.
 2. The method for hand-over of a terminal according to claim1, further comprising: maintaining a pilots mapping table including atleast a pilot code of CDMA and a pilot code of EV-DO for each bordercell.
 3. The method for hand-over of a terminal according to claim 1,said pilot code comprises pseudo noise code.
 4. The method for hand-overof a terminal according to claim 1, wherein said step of calculatingCDMA pilot strength based on said EV-DO pilot strength comprises:calculating CDMA pilot strength based on said EV-DO pilot strength and aratio of a pilot power to overall power at antenna port in CDMA cell. 5.The method for hand-over of a terminal according to claim 4, whereinsaid ratio of a pilot power to overall power at antenna port in CDMAcell is defined as:$\frac{f*( {P_{OH} + P_{T}} )}{P_{OH} + {\beta\mspace{11mu}\max*P_{T}}},$in which f is a ratio of a pilot power to a CDMA cell's maximumtransmitter power, P_(OH) is a power of overhead channel of the CDMAcell, P_(T) is a total traffic power available for the CDMA cell, βmaxis the maximum call load factor for the neighbor cells.
 6. The methodfor hand-over of a terminal according to claim 1, said step oftransmitting an EV-DO pilot signal comprises: generating an EV-DO pilotsignal at said second base station.
 7. The method for hand-over of aterminal according to claim 6, said step of generating an EV-DO pilotsignal comprises: generating pseudo noise sequences of EV-DO for I and Qchannel respectively based on an offset of pilot pseudo noise andtransmitting time advance (Tx) provided by a controller of said secondbase station; baseband filtering said PN sequences for I and Q channelrespectively; and Carrier modulating the PN baseband sequences for I andQ channel to obtain real signal from PN sequences for I and Q channel.8. The method for hand-over of a terminal according to claim 7, saidstep of generating an EV-DO pilot signal further comprises: gating saidsequences for passing 96 chips of 1024 chips within half slot andsetting the remainder 0 for I and Q channel respectively.
 9. The methodfor hand-over of a terminal according to claim 7, said step ofgenerating pseudo noise sequences uses two phase-shift registers for Iand Q channels respectively.
 10. The method for hand-over of a terminalaccording to claim , said step of generating pseudo noise sequencescomprises: judging the PN sequences for I and Q channel respectivelybased on system clock to output 96 chips of 1024 chips within half slot.11. The method for hand-over of a terminal according to claim 7, saidstep of generating pseudo noise sequences comprises: multiplying saidreal signal with pilot gain after the step of carrier modulating.
 12. Anetwork element for controlling hand-over from a first base station to asecond base station, wherein said first base station is EV-DO enabled inan access network and said second base station is not EV-DO enabled,comprising: calculating unit configured to calculate a CDMA pilotstrength based on an EV-DO pilot strength of said second base stationwhich is not EV-DO enabled; determining unit configured to determinewhether said CDMA pilot strength is above a hand-over threshold; andperforming unit configured to perform the hand-over of a terminal fromsaid first base station to said second base station when said CDMA pilotstrength is above the hand-over threshold.
 13. The network elementaccording to claim 12, further comprising: maintaining unit configuredto maintain a pilot mapping table including at least a pilot code ofCDMA and a pilot code of EV-DO for each border cell.
 14. The networkelement according to claim 13, said pilot code comprises pseudo noisecode.
 15. The network element according to claim 12, wherein saidcalculating unit calculates CDMA pilot strength based on said EV-DOpilot strength and a ratio of a pilot power to overall power at antennaport in CDMA cell.
 16. The network element according to claim 15,wherein said ratio of a pilot power to overall power at antenna port inCDMA cell is defined as:$\frac{f*( {P_{OH} + P_{T}} )}{P_{OH} + {\beta\mspace{11mu}\max*P_{T}}},$in which f is a ratio of a pilot power to a CDMA cell's maximumtransmitter power, P_(OH) is a power of overhead channel of the CDMAcell, P_(T) is a total traffic power available for the CDMA cell, βmaxis the maximum call load factor for neighbor cells.
 17. A hybridterminal for use in a CDMA system and an EV-DO system, wherein saidhybrid terminal is configured to receive an EV-DO pilot signal from saidCDMA system via a base station which in not EV-DO enabled.
 18. A devicefor generating a pilot signal, which is to be equipped with a non-EV-DOenabled base station in a CDMA system, wherein said device is configuredto generating a EV-DO pilot signal.
 19. The device for generating apilot signal according to claim 18, wherein said device comprises:generating module configured to generate pseudo noise(PN) sequences ofEV-DO for I and Q channel respectively based on an offset of pilotpseudo noise and transmitting time (Tx) advance provided by a controllerof said second base station; baseband filters individually configured tobaseband filter the PN sequences for I or Q channel; and Carriermodulating module configured to obtain real signal from PN sequences forI and Q channel.
 20. The device for generating a pilot signal accordingto claim 19, wherein said device further comprises: gating modulesconfigured to gate said sequences for passing 96 chips of 1024 chipswithin half slot and setting the remainder 0 for I and Q channelrespectively.
 21. The device for generating a pilot signal according toclaim 19, wherein said generating module comprises phase-shift registersfor I and Q channel respectively.
 22. The device for generating a pilotsignal according to claim 19, wherein said device further comprises:multiplier configured to multiply the real signal provided by said QPSKmodulating module with pilot gain.
 23. The device for generating a pilotsignal according to claim 19, wherein said generating module comprisesoutput judging modules for I and Q channel respectively, configured tojudge the PN sequences for I or Q based on system clock for outputting96 chips of 1024 chips within half slot.
 24. A device according to claim18 implemented in a base station in a CDMA system, which is not EV-DOenabled.
 25. A network element according to claim 12 implemented in acommunication system comprising a hybrid terminal configured to receivean EV-DO pilot signal from a CDMA system and a base station in the CDMAsystem, which is not EV-DO.